Anti-inrush sensing device



r Jan. 21, 1958 R. STEINER 2,820,927

ANTI-:NRUSH SEN SING DEVICE Filed May 28, 1956 I 2 Sheets-Sheet 1 3,6Fig. 1

INVENTOR. RUDOLF STEINER BY I TTORNEYS R- STEINER ANTI-'-INRUSH SENSINGDEVICE Jan. 21, 1958" 2 Sheets-Sheet. 2

Filed May 28, 1956 kamkkbb INVENTOR RUDOLF STEINER United States PatentANTI-INRUSH SENSING DEVICE Rudolf Steiner, Van Nuys, Calif.

Application May 28, 1956, Serial No. 587,914

8 Claims. (Cl. 317-49) (Granted under Title 35, U. S. Code (1952), sec.266) This invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The invention relates to an anti-inrush sensing device, and moreparticularly to an anti-inrush sensing device for use with electricalcircuit breakers.

In electrical systems, the steady state conditions for various circuitfactors are frequently the exception rather than the rule. Certainallowances are made for the socalled normal variations of the voltage orcurrent that can be tolerated without damage to wiring, power sources,and equipment. If these variations exceed specific limits, up and/ordown, situations detrimental to the proper functioning or the safety ofthe system may develop and devices must be provided which either limitthe deviations or disconnect the faulty element from the system.Undercurrent protection devices are less important as a rule, andtherefore application of these devices in electrical power systems findsomewhat less utility. Over-current protection devices, on the otherhand, or those designed for response upon over-voltage or over-currentdeserve first consideration.

Various over-current devices are in existence. It is generally requiredof such a device not only that it distinguish between a dangeroussustained overload and a transient overload, but that it also isinsensitive to such a transient overload, more commonly known in thepopular language of the trade as a nuisance type of overload. Thesetransient overloads, characteristically of short duration, are harmless,and various means have been devised to preclude circuit openings duringnuisance overloads. Typical of such devices has been the utilization oftime delay response elements in a variety of complex electromechanical,and electrical and hydraulic constructions, which include, for the timedelayresponse characteristic, such members as oil dash pots, inductiontype rotatably driven disks in which the duration of the time delay isdetermined by the amount of rotation of the disk, or the series-parallelcombination of electrical RLC elements. A further type employs a relayarrangement based upon the principle that transient or nuisanceoverloads are predominately either of negative or positive polarity. Acommon disadvantage of the aforementioned protective devices is thattheir response to dangerous overload currents is frequently tooslow-acting, and generally there are more mechanical components than aredesirable for good design and reliability of performance. Further, ifhydraulic fluids are involved, additional difiiculties may arise due tothe effects of the environments in which these devices may be employed.

ice

The anti-inrush sensing unit contemplated by the instant inventionsubstantially overcomes the various deficiencies of the aforementionedprotective devices, The inventive device utilizes in a simple andcompact construction the inductive character of a pair of coils whichare of substantially differing values of inductance to precludeoperation in response to the fast-rising or nuisance type of current orvoltage overload. One coil is essentially an aircoil inductance, whilethe other is enclosed by an iron-core magnetic circuit. An embodiment oftwo such inductive coils in a parallel circuit arrangement is used todiscriminate against surge or inrush currents of the nuisance type so asto preclude circuit openings, while in the event of dangerous sustainedoverload currents the tripping arm of the inventive device is efiectiveto open a circuit breaker or other protective mechanism, since theinductive effect of the iron-core coil is rapidly reduced by thepresence of magnetic core saturation and/ or a rapidly decreasing rateof change of current. Therefore, an embodiment of the anti-inrushsensing element according to the inventive principle substantiallyovercomes the deficiencies of the prior art by enabling a simple compactconstruction requiring a minimum of electro-mechanical components, thuscontributing to a high degree of reliability of performance. Inaddition, this anti-inrush sensing device is more universal inapplication than the existing devices of the prior art, since theinventive device is applicable to power circuits employing eitheralternating or direct current.

An object of the present invention is the provision of an anti-inrushsensing device which will distinguish between a dangerous sustainedoverload current and a transient overload current.

Another object is to provide an anti-inrush sensing device having anadjustable core to permit calibration of the magnetic circuit incompliance with specific, unforeseen circuit parameters.

A further object of the invention is the provision of an anti-inrushsensing device which will discriminate against fast-rising nuisanceoverload currents, but will respond to dangerous overload and faultconditions by actuating an armature having a trip arm.

A final object of the present invention is the provision of ananti-inrush sensing devicew hich has universal application, beingadapted to either alternating or direct current. Other objects and manyof the attendant advantages of this invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawing in which like reference numerals designate like orcorresponding parts throughout the figures thereof and wherein:

Fig. 1 is a simplified view partially broken away, showing a preferredembodiment of the anti-inrush sensing device of the instant invention.

Fig. 2a illustrates a graphic representation of a typical magnitude ofinrush current upon initial application of a load to a D. C. powercircuit relative to its subsequently assumed steady state value.

Fig. 2b illustrates a graphic representation of a typical inrush currentwhich may appear on a line and is capable of developing into a dangerousfault during regular operation.

Fig. 3 is a schematic representation of one circuit embodiment of theanti-inrush sensing device showing the manner in, which" the respectivecoils may be connected for aiding-fluxa Fig. 4 is a schematicrepresentation of an alternate cir cuit embodiment of the anti-rushsensing device showing the manner in which the respective coils may beconnected for opposing flux.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in the functional embodiment of Fig. 1 an upper coilencircled by a substantially closed magnetic circuit consisting of anupper supporting frame 25, including a verticalmember 12 and ahorizontal member 14, which may be formed integrally with member 12 orbefixedly secured thereto by any suitable fastening, an adjustablypositioned core-16, anair gap 18, and an armature20, which'is confiedinto an area ofinfluence adjacent the. pole face of'core 16 byadjustable stop-22 and lock nut 24, both of which are secured to astationary portion of frame 23 which may conveniently be a part of. ahousing for the inventive The elements comprising the magnetic circuitof the upper coil 10 areof highly permeable material such device.

as soft iron, or'the like, and may preferably be a laminated type ofconstruction. A spring 26 fixedly secured to upper frame 12 by means ofa rivet 35'or other suitable means biases the armature 20, tension onwhich is 'ad-' justable by means of screw 28 threadably engaged in thearmature and locked with locking nut 30. The armature pivots about pin32 when the armature'is attracted to the pole face of core 16, and themovement of tail piece of the armature assembly is effective tointerrupt a circuit breaker or other protective mechanism. The lowercoil 40 is an air-core inductance, the lower supporting frame 19for thiscoil being of a non-ferrous material such as brass, or the like. bejoined to its companion member, the upper supporting frame 25, by meansof a suitable fastener such as a screw 21, as shown. Permeable core 16is threadably engaged with a relatively slenderadjusting screw 36having. nonmagnetic properties, and is fixedly secured with pin 44. Anon-magnetic collar 42 may be provided, as shown, as a lower limit stoplocked in position with set screw 43 on adjusting screw 36, which itselfis threadably engaged in lower frame 19 and locked with lockingnut 38.Hence, the highly permeant core 16 is restricted in its travel,preventing entry thereof into the air-core inductance 40 when rotationof screw 36 resultsin vertical movement of the core within the'tubularnon-ferrous coil bobbin.45' on,

which coils 10..and 40 are wound. Horizontal members 46 are inflexiblenon-ferrous separators provided for PUT-1 poses of insulation and mayconveniently be fiber washers.

It should be noted that although there is a small amount of leakageflux. originating frjomthe lower coil whichis permeable material ,to,give the device different leakage flux characteristics.

To, appreciate or, better, understand the principle of operation of theanti-inrush sensing .device,.it is desirable to referinitiallyto.Fig.,2a.and;.Fig,-2b.., First,: it is believed to beself-evident that, the. instant invention constructedf'as shown. insFig;1 will, respond .to a gradual, in:

creasein current to a point above the upper responselimit designated inFigs. v.2a,,and, 2b .by,roman..numeral I by generatinga.suificiently.strongfiunto; close the armature;

The lower supporting frame 19 may 34-which conveniently may be formed asan integral part 4 20, noting that the amount of inductance in therespective coilsis not-a significant factor when the rate of increase incurrent represented by the slope of the current wave is small. Hence, ashallow current curve representative of this condition is notillustrated in Figs. 2a and 2b. Conversely, Figs. 2a and 2b constituteillustrations of typical transient or nuisance current overloadscharacterized by a high constant rate of change of current indicated bythe steep slope of the curves. There are various circumstances in whichthe normal course of operation may cause quite excessive over-currentsto flow, as shown, though for a comparatively short period of time. Twotypical representatives of such occurrences are the current surges orinrushes experienced upon initially connecting a tungsten-filament lampload to a line, or when starting an electric motor. In each case,the-current may rise to 6 to 10 times thenormal, ratedoperatingcurrent.Such a condition is illustrated by the curve III in Fig. 2a. Similarconditions caused by circumstances other than those reiterated above,may occurduring thetoperation of an equipment, as portrayed by the curveIV in Fig. 2b. Contrary tothese nuisance overloads,.dangerous overloadand fault conditions can develop from what initially appears to be atemporary nuisance overload. This condition is represented by the dottedcurve V in Fig. 2b. In this instance,- the current' initially risessubstantiallyin thesame manner asif it were anormal surge of shortduration;

however, it keeps on increasing past the crest C'until the magnitude ofthis current; is only prevented from reaching an infinitevalue'throughthe physical and electrical properties of-the circuit atwhich the slope decreases substan tially to zero. It becomes clear thatboth the crest of theharmless surge and the entire trace of thedangerous.

overload current are well beyond and above the upper response limit I of"the over-current sensing meansrof the instant invention, and it furtherbecomes clear. that. a close relationship exists amongthe initial. trendof a,

nuisance overload and a dangerous overload. In fact, the first portionof both these manifestations is, identical. It finally becomesapparentthat. the decision in regard to what transpires (nuisance ordangerous overload) can only be made in retrospect,.when it becomesapparent at point C whether the current will fall along the solid traceIV or continue to. rise along. thev dotted traceV.

It is the'characteristics peculiar to these manifestationsof transientoverload conditions illustrated in Figs. 2a and- 2b upon whichtheprinciple of operation of .theinventive anti-inrush sensing devicedepends. In, contrast. to thegradually developing overloadvconditionreferred to abovewherein inductance was not a significant factor, the.rela-. tive inductance of the respective coils of theinstant inventionis a critical factor in its operation in, response to theserapidly developing transient overloads. A fundamental property of aninductance is ,thattheinduced.elec

tromotive force is equalftothe inductance times-therate of change ofcurrent, or stated more-precisely 3 The steep slope of the.current surge,up to point C ,or, the

substantially constant: rate ofchange .of ,current permitted1to increasesufficiently to generate afluxlarge,

enough to .close armature 20in response to a, dangerous overload, andthus, thedevice functions in a manner comparable to that in which itresponds to an overload curin essence,

producing a self-induced rent developed more gradually along a shallowslope to the upper limit response I, as described above. As in the caseof a dangerous overload, the steep slope presented by a current wavefront in the case of a harmless surge or transient overload generates incoil 10 a self-induced E. M. F. of sufiicient magnitude to prevent anyincrease in flux across the gap, thus precluding response of thearmature to these nuisance type current overloads, while conversely, theabrupt reversal of slope of curve IV at point C to a steep negativeslope characteristic of a transient nuisance overload is accompanied bya reversal in the sense of the self-induced counter E. M. P. whichmerely perpetuates the relatively very small current fiowing in coil 10insufficient to effect operation of armature 20 in response to atransient overload. Consequently, inductance of the coil 10 is effectiveto discriminate against nuisance overload currents by virtue of itsreaction to a rate of change of current which is an inherentcharacteristic of any surge or transient current.

The actual operation of the inventive device can best be described withreference to Fig. 3 which illustrates a schematic representation ofparallel aiding circuit connections of the anti-inrush sensing element.As shown in the functional embodiment of Fig. l, the arrangement shownis composed of two coils, an upper iron-core inductance 10, and a lowerair-core inductance 40, which together comprise the binary actuatingmeans of the inventive overload sensing device. Armature 20 is shownresting in its normal quiescent position biased against stop 22 byspring 26 affording a greatly exaggerated showing of air gap 18. Theincoming line 11 is shown connected at junction 15 to coils l and 40, inturn connected at point 17 to the common outgoizg line 13. The parallelconnection of coils 10 and 40 as depicted in Fig. 3 permits the fluxesto combine in an additive or like sense, the schematicallyrepresentative leakage flux common to both coils is indicated by thedirection of arrows to be in the same sense as 5,, and the schematicallyrepresentative fluxes, respectively, of the upper and lower coils. Toillustrate the operation of the device, assume as an example, that thetwo common lines 11 and 13 are capable of carrying 10 amperes continuously,-where as each coil 10 and 40, respectively, being wound of anidentical number of turns of like wire, carries one-half of the total,i. e., 5 amperes continuously. Thus, during a steady state currentcondition, the total of amperes will divide evenly, and armature 20,calibrated by means of its spring 26' to remain in the open positionshown, will not respond to the coil current of 5 amperes. On graduallyincreasing loads which exceed the upper response level I, the totalcurrent will separate equally in the previously described manner,however, the lines of magnetic flux emanating from the pole face of core16 will now attract the armature sufficiently to overpower biasingspring 26'. Consequently, the armature tail piece 34 will rotate withthe armature and engage tripping or other release means and cause theautomatic interruption of the the circuit in series with which the lines11 and 13 were originally connected.

On sudden surges, inrushes or the like, of comparatively short duration,the incoming total current will no longer be divided evenly among thecoils 10 and 40, for the inductance of the iron-core equipped coil ismuch greater than that of the air-core coil. Thus, a large portion ofthe total current will flow through coil 40. A strong field results fromthe flow of current through coil 40, but because it is physically remotefrom armature 20 and not surrounded by a magnetic circuit, little effectwill be produced by the increase in leakage flux on thearmature 20. If,however, the apparently temporary current surge should develop into avicious fault, in which case the self-induced counter E. M. F. of coil10 falls to zero, the armature 20 will be attracted, after a fewmilliseconds, by the combined effect of the remote field of coil 4% andthe now increasing field o of coil 10.

A useful modification of the basic arrangement is illustrated,schematically, in Fig. 4. Contrary to the circuit embodiment describedabove, coil 40 is wound in the opposite sense with respect to coil 10 asindicated by the wiring symbols. Aside from this difference, all othercircuit and construction elements used previously are again employed andhence the showing in Fig. 1 is equally applicable to this embodiment.The operation of this unit is comparable to that pictured in Fig. 3,except that on surge or inrush currents, not only does the major portionof the current flow through coil 49 but the magnetic fluxes and createdthereby, will be opposed to flux induced by coil 10, as indicated by therelative directions of the schematically representative flux lines inFig. 4. The leakage flux 1: will under these conditions, detract fromthe total flux that is emanating from the pole face of core 16, andtherefore, more time will elapse before the net flux required to attractthe armature 2G with sufficient force to overpower the biasing spring26' is developed than that needed previously for the aiding fluxconnection of Fig. 3. A need for such an embodiment of the instantinvention may arise on starting of electric motors having inrushcurrents of comparatively longer duration than, for example,tungsten-filament lamp load starting currents. It should be noted thatdangerous overloads will, as in the other embodiment, cause displacementof the armature in response to the flux generated either by theover-energized coil 10 or by the physically remote, reverse-wound coil40, or the comhined effect of both. Since only soft iron, or a metal ofsimilar characteristics is used for the parts of the magnetic circuit,the reversal of the magnetic polarity has no bearing on the operation ofthe device characterizing the instant invention.

It is apparent from the foregoing description of the alternativeembodiment of the anti-inrush sensing device that a wide variation oftime delay characteristics are possible, by providing for a leakage fluxgb which is of an intensity comparable to the desired time delay. Theconstruction in Fig. 1 provides for one type of embodiment, but otherconfigurations providing for different intensities of leakage flux 5,,are well within the skill of those in the art. For example, an elementconstituting a permeant path to intensify the leakage flux may beprovided between the core at the lower end of coil 40, as shown in Fig.1, and a point adjacent the free end of armature 20, or alternatively byforming the lower supporting frame 19 of a permeable material. In thisrespect, it should be pointed out that the leakage flux as shown for theaiding flux connection in Fig. 3 is not essential for that particularmode of operation. The represented leakage fiux is inherent in theconstruction of the illustrative functional embodiment, and its presenceis advantageously utilized in the alternative construction, as describedin relation to Fig. 4.

Although the invention has been described from a point of view ofapplication to direct current circuits, the principles evolved will holdtrue, in essense, for application of the anti-inrush sensing device toalternating current circuits having frequencies from 25 throughapproximately 1000 cycles per second. The illustrative curves of Fig. 2aand Fig. 2b, under alternating current operation, are readilyrepresentative of qualitative root-mean-square values of current.Further, so far as the magnetic circuit is concerned, its physicalcharacteristics will depend on the contemplated application of thesensing unit. While the conditions for direct and 25 through 60 cyclealternating current will be comparable within reason, those for higherfrequency alternating current applications will require specialconsideration, inasmuch as the impedance of a coil varies directly withthe applied frequency, and hence, is a significant factor whencontemplating operation in a frequency range beyond the usual powerfrequencies.

An embodiment of the anti-inrush sensing device acof a dangeroussustained overload current, an armature connected to a suitable trip armis effective to interrupt a circuit breaker or other protectivemechanism. Its construction-provides for incorporating such desirablefeatures as an adjustable core, variable armature biasing pressure, anda variable air gap, all of which contribute to the adaptability of thesensing device in various applications by permitting calibration of themagnetic circuit in compliance with specific circuit parameters. Theanti-inrush sensing device is further unique in that it is of universalutility, being capable of operating in both direct and alternatingcurrent circuits.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and thatnumerous modifications or alterations may bemade therein withoutdeparting from the spirit and the scope of the invention as set forth inthe claims.

What is claimed is:

l. ln an electrical power system having a main power line for supplyingexcitation to a load, an overload sensing device comprising, incombination, a first relatively high inductance means, a secondrelatively low inductance means, said inductance means beinginterconnected electrically in'parallel and thence connected directly inseries with a load to form binary actuating means of said sensingdevice, and armature means pivotally mounted adjacent said first highinductance means for movement between an open position and a closedposition, said armature means being insensitive, to transient or surgeoverload currents through said inductance means, but responsive tosustained overload currents through said inductance means, therebyactuating said armature means to the closed position.

2. An overload sensing device comprising, in combination,'a firstrelatively high inductance means, and a second relatively low inductancemeans, said first and said second inductancemeans'being electricallyconnected in shunt and disposed on a common axis for magnetic fluxinteraction, and an-arrnature with permeable supporting means therefor,forming a substantiallyclosed.magnetic circuit with said first highinductance means, said armature being movable between an open positionand a closed position, saidarmature being insensitive to transient orsurge overload currents through said inductance means, but responsivetosustained overload currents through said inductance means, therebyactuating the armature to the closed position 3; An anti=inrush sensingdevice comprising, in com v bination,- afirst inductance means, a secondinductance means; said inductance means being electrically connected inparallel, permeablecore means adjustably movable withinthe core ofsaidfirst inductance means, andjan armature with an elongatedpermeable'supporting means therefor, forming a'substantially closedmagneticcircuit with said permeable core means, said armature being.

movable betweena normally-open position and a closed position, andinsensitive to-transient or'surge overload currents through saidinductance means, but responsive to sustained overload currents throughsaid-' inductance means, thereby actuating'said armature to the closedposition.

4; Ananti-inrush sensing device comprising, in combination, afirstrelatively high-inductance means, a second relatively-low inductancemeans, said inductance means being connected electrically in parallel,said first high inductance means including apermeable core meansarmounted for movement between an open and a closed POSIUOH, permeablesupporting means for said armature means, and biasing means effective tomaintain saidannature; meansin' its normally open position, saidarmature means and said'permeable supporting means forming asubstantially closed magnetic circuit with said core means, saidarmature means being insensitive to transient or surge overload currentsthrough said inductance means, but responsive to sustained overload.currents through said inductance means bymovement to its closedposition.

5.-An-anti-inrushsensingdevice comprising, in com bination; a firstrelatively high inductance means, a second relatively low inductancemeans, said Iinductance means being electrically interconnected inparallel, said second lowinductance means being disposed adjacent to andon a commonaxis withsaid first inductance means, and unilaterallymagnetically coupledfwith said first inductance means, an armature andpermeable supporting means therefor, said armature being rotatablymounted for movement between an open and a closed position,

biasing means effective to maintain said armature in its normally openposition, andJa trip arm means connected to said armature and capable ofreleasing a circuit breaker or other protective-mechanism, said firsthigh inductance means including a permeable core adjustable for limitedtravel along'the core of said first high inductance means, saidpermeable coreand said armature and the permeable supporting meanstherefor comprising elements of a substantially closed magnetic circuit,said second 'low inductance means, having an air-core and including asupporting frame of non-magnetic material, said armature beinginsensitive to transient, or surge overload currents through saidinductance means, but, responsive to. sus tained overload currentsthrough said inductance means by movernent 'to its closed position,effectinga displace-j ment of said trip-armmeans.

6. An anti-inrush=sensing device comprising; in combination, a firstrelatively high-inductance means, a second relatively low inductancemeans, said inductance means being electricallyinterconnected inparallel, said second low inductance means being disposed adjacent toand on a common axis with said first high'inductance means andunilaterally magnetically coupled with said first high inductance means,anarmature and permeable supporting means therefor, said armature beingrotatably mounted for movement between an open and a closed position,biasing means effective to maintain said armsture in its normallyopen'position, and a trip arm means connected to said armature andcapableof releasing a circuit breaker or other protective mechanism,said first high inductance means including a permeable core meansadjustable for limited movement along the core. of said first highinductance means,- said second low inductance means having an-air-coreand-including a magnetically permeable'supporting frame, said permeablecore means being adjustablyconnected by non-magneticmeans to one end ofsaid permeable supporting frame, said armature being insensitive totransient or surge overload currents through said inductance means, butresponsive to sustained overload currents through said inductance meansby movementto its closed position, effecting displacement of said triparm means.

7. An overload sensing device comprising, in combination, a firstrelatively highinductancemeans, a second relatively low inductancemeans, said first and said second inductance means being; disposedmutually adjacent on a common axis and electrically connected formagnetic coupling in a concurrent aiding sense, and an armature withpermeable supporting means therefor forming a substantially closedmagnetic circuit with said first relatively highjinductance-means, saidarmature being movable be tweenan open position and a closed position,said arma! ture being insensitive to transient or surge overload cubrents through said inductance means, but responsive to sustainedoverload current through said inductance means.

8. An overload sensing device comprising, in combination, a firstrelatively high inductance means, a second relatively low inductancemeans, said first and said second inductance means being disposedmutually adjacent on a common axis and electrically connected formagnetic coupling in an opposing sense, and an armature with permeablesupporting means therefor forming a substantially closed magneticcircuit with said first high in- 10 ductance means, said armature beingmovable between an open and a closed position, said armature beinginsensitive to transient or surge overload currents through saidinductance means, but responsive to sustained overload current throughsaid inductance means.

References Cited in the file of this patent UNITED STATES PATENTS1,873,087 Wensley Aug. 23, 1932 FOREIGN PATENTS 217,065 SwitzerlandSept. 30, 1941

